People with sleep apnea are dangers on the road, according to new research presented at the 2013 Sleep and Breathing Conference in Berlin. The findings suggest that people with untreated sleep apnea are more likely to nod off while driving and more likely to fail driving simulator tests than people without sleep apnea.

Meir Kryger, MD, assistant professor of pulmonary medicine at the Yale School of Medicine, said the findings indicate that those with sleep apnea need to recognize their condition -- and stick to the prescribed treatment regimen.

"The No. 1 reason people with sleep apnea are referred to a clinic is because of daytime sleepiness," he said. "When people are sleepy, they may be okay at short tasks, but if they need to do something that requires a lot of attention for a long period of time, such as driving, they'll often make mistakes."

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People with sleep apnea have abnormal breathing pauses during sleep, which can cause them to wake up as much as 30 times or more per hour in order to resume normal breathing. Symptoms vary, but may include snoring and being tired throughout the day. Between 80 to 90 percent of people with sleep apnea are undiagnosed, according to the American College of Physicians, and many people don't realize they have the condition until a bed partner notices their abnormal breathing.

Previous research linked sleep apnea to an increased risk of traffic accidents, so researchers from University Hospital in the United Kingdom conducted two studies to determine why. In the first, they had 133 people with untreated sleep apnea and 89 healthy controls take part in a driving simulation. The participants were judged on a variety of conditions, including the ability to complete the test, the amount of time spent in the middle lane, and whether they crashed. They found that 24 percent of people with sleep apnea (32 people) failed the test, compared to only 12 percent of the control group (11 people).

"In the first study, although some people in the control group also failed the test, there were several key differences in the reasons for failure," study author Mark Elliott, MD, sleep breathing specialist at University Hospital, said in a statement. "For example, 13 patients were unable to complete the test because they fell asleep [and] veered completely off the motorway and 5 patients [failed] because they spent more than 5 percent of the study outside the lane that they had been instructed to remain in. No controls failed for either of these reasons."

The second study involved 118 patients with untreated sleep apnea and 69 healthy controls who filled out a questionnaire before taking the driving test. On the questionnaire, 35 (41) percent of patients with sleep apnea admitted to nodding at the wheel, compared to 11 percent of the control group (8 people). Thirty-eight percent of patients with sleep apnea (45 people) failed the driving test. None of the people in the control group failed the driving test in the second study. (Neither of the studies have been peer-reviewed.)

The study looked at patients with untreated sleep apnea, but according to Dr. Kryger, sleep apnea patients who have the condition under control are not likely to be a risk on the road. But he noted that some treatments for sleep apnea, such as continuous positive airway pressure (CPAP) machines, require the user to wear a mask while they sleep and can be uncomfortable, leading to noncompliance.

"People that are untreated or not adhering to their treatment are the real hazard," said Kryger. "Some new treatments even have a built-in sensor to ensure that people are actually using it. We can tell pretty easily now whether patients are actually using their treatment."

Kryger added that the findings underscore the need for better and earlier diagnosis of sleep apnea.

"There are still a lot of doctors who do not routinely ask questions about whether sleep apnea is a possibility," he said. "In my opinion, everyone who goes into a medical office should be asked about their sleep habits, and whether they're sleepy during the day or snore at night."